import React, { Component, createRef } from 'react'
import Test from './Test'

export default class App extends Component {
  

  render () {
    
    return (
      <div>
        App <button onClick={()=>{
          this.forceUpdate()
        }}>强制更新</button>
      </div >
    )
  }
 
  componentDidUpdate () {
    console.log('2，componentDidUpdate')
    // console.log(document.querySelector('span').innerHTML)
  }
}
